Friction clutch rheostat



Feb. 2, 1937. c. J. HATHORN 7 2,069,440

FRICTION CLUTCH RHEOSTAT Filed July 25, 19:55 4 Sheets-Sheet 1 J .1 F1,17 T 71% 6 W INVENTORY Clar n'ce r1 [int/writ,

B Y Q 3; A TTORNE Y.

Feb. 2, 1937. c. J. HATHORN 2,069,440

FRICTION CLUTCH RHEOSTAT Filed July 25, 1935 4 Sheets-Sheet 2 INVENTOR.

Clarence 11M horn,

A TTORNE Y.

Feb. 2, 1937. c. J. HATHORN FRICTION CLUTCH RHEosTA'r Filed July 23,1935 4 Sheets-Sheet 3 IN VEN TOR.

m H J m TTORNEY.

Feb, 2, 1937.

c. J. HATHORN 2,069,440

FRICTION CLUTCH RHEOSTAT Filed July 23, 1935 4 Sheets-Sheet 4 0-100 I.11. do 306 310 G 3416 3373 350 30 316' 3:1 G j? r j 12 l I Z H A1 1 217K I by? INVENTOR.

' M Ularence' rfflalfiorn,

. ATTORNEY.

Patented Feb, 2, 1937 PATENT. OFFICE 2,069,440 FRICTION cnn'rcnansos'rs'r- Clarence J. Hathorn, St. Marys, 1%., minor to The StackpoleCarbon Company, St. Marys, Pa., a corporation of PennsylvaniaApplication July 23, 1985, Serial No. 32,717

9Claims.

-My invention relates to an adjustable resistance device and relatesmore particularly to a device for controlling the intensity of sound orthe tone of sound in radio receiving circuits or public addressingsystems.

Heretofore, it has been customary to employ a volume control for anautomobile radio system which is actuated from a flexible shaft, thelatter having one end connected to a knob on the con- 10 trol head whichmay be mounted either upon the dash board or upon the steering column,and the other end connected to the control shaft of the volume control.The snap switch in certain cases has been mounted and controlled inde- 5pendently of the volume control. Therefore, in

automobile radio sets employing a separately controlled switch and aseparately controlled volume control, difllculty of properlysynchronizing the switch and the volume control has been experienced.

Since a flexible shaft of considerable length generally must be employedto operate the volume control, the flexible shaft, of sui'licientstrength to withstand the maximum turning a torque applied to the knob,is quite expensive. To reduce the strength of the flexible shaft, whichgenerally comprises multiple layers of closely coiled wires, and stilluse the old type of volume control would result in' kinking or sodistorting the flexible shaft when an excessive turning torque would beapplied.

In rheostats or volume controls which are key controlled and where theshaft is limited in rotation, an excessive turning force occasionallyrotated 360 or more in either a clockwise or a counterclockwisedirection.

45 It is another object of my invention to construct a friction clutchvolume control or adjustable resistance device which may be actuated inthe customary manner, i. e. by a clockwise or counterclockwise turningmoment.

6 Another object of my invention is to employ a volume control which maybe readily synchronized with a separately mounted and separatelycontrolled snap-switch.

Another object of my invention is to construct 55 a volume control.which may be actuated by a light and inexpensive type of flexible cablewithout resulting in the flexible cable kinking or being permanentlydistorted.

Another object of my invention is to construct a clutch between therotatable control shaft and 5 the pressure member which is eiiicient inoperation.

Another obiect of my invention is to construct a contact member for theresistance element which is positive in action and which burnishes 1 orslides frictionally in engagement with the resistance element.

Another object of my invention is to construct a movable contact shoe orcurrent collector which will adiust itself to any irregularitiesappearing upon the surface of the resistance element which will notcause undue abrasion between the contact shoe and the resistanceelement.

Another object of my invention is to construct an inexpensive 'eflicientrotary current collector between the pressure arm and the stationarycurrent collector for the derived circuit terminal.

A still further object of my invention is to construct an inexpensivecombinedspacer and tuming coupling between the volume control and thefriction disc.

Another object of my invention is to construct tandem arranged volumecontrol units actuated from a single control shaft having an interposedfriction clutch.

Another object of my invention is to construct two tandem arrangedvolume control units actuated from a single control shaft and having asingle spring for applying pressure to each of the two volume controls.

Another object of my invention is to construct a snap switch operablyactuated by a rotatable control shaft wherein a friction clutch isinterposed between the snap switch mechanism and the control shaft. 40

Another object of my invention is to construct a, combined adjustableresistance device and switch unit, both of which are actuated by asingle control wherein a clutch is interposed between the control andthe resistance device and 5 switch mechanisms.

Other objects of my invention are to construct an improved device of thecharacter described which is readily and economically produced, that issturdy in construction, and which has a maximum degreeof emciency inoperation.

with the above and related objects in view, my invention consists in thedetails of construction and combination of parts, as will be more fullyunderstood from the following description when read in conjunction withthe accompanying drawings, in which:

Fig. 1' is a fragmentary sectional side elevational view of anadjustable resistance deviceor.

volume control embodying my invention.

- Fig. 1.

-Fig. 7 is a modification of the volume control head and friction clutchshowing only the control shaft, the friction clutch, the pressure arm onthe control head, and the rotary brush.

Fig. 8 is a sectional view taken on the line 8-8 of Fig. 7 illustratinga modification of the pressure arm.

Fig. 9 is a sectional view taken on the line 88 of Fig. 7 illustrating amodification of the sliding contact member for the derived circuit.

- Fig. 10 is a fragmentary side elevational view of a midget type ofdual volume control with a helical spring-type of friction clutch.

Fig. 11 is a fragmentary sectional view of a midget type of dual volumecontrol, arranged in tandem, with spring-type of friction clutch andswitch, all controlled from a single shaft.

Fig. 12 is a sectional view taken on the line i2-l2 of Fig. 11. Fig. 13is a plan view of the snap switch.

' Fig. 14 is a perspective view of the snap switch in its open circuitposition.

Referring now in detail to the drawings, 1 show a friction clutchmounted upon a volume control or adjustable resistance device, the unitcomprising a molded base, generally designated as A, of insulatingmaterial, such as material known under the trade-mark Bakelite. The baseis substantially a disc-like member having a central aperture throughwhich a control shaft i8 extends. Defining the central aperture is acylindrical bore l2 of a diameter slightly in excess of the diameter ofthe shaft l8, and an internally threaded bore M for receiving theexternal threads i8 of one end of a shaft bushing l8. The bushing l8holds the entire volume control on a mounting panel (not shown) bymeanspf a lock-nut-this is the well-known single hole volume controlmounting.

A boss 28 is formed integrally with the outside flat surface of the baseA so that the annular flat surface 22 of the boss abuts against amounting panel (not shown) to space the volume control from the mountingpanel. This arrangement precludes the electrical terminals 22, 28. 25,which are mounted in grooves on the minor peripheral surface 22 of thebase, from being short circuited when the unit is mounted upon a metalpanel. A stud 21 is integrally formed with the base and is adapted to itinto a complementary opening on the mounting panel to prevent rotarymovement of the rheostat with respect to the mounting panel, whichmightresuit in the breaking or short circuiting of the lead wiresconnected to the terminals. Upon the inner surface of the base'ls asmallcircular boss 28 whose outermost surface is engaged by a washer 28 tolimit the movement. of the shaft in one direction (as hereinafter willbe more fully aoeaseo Fig. 3 is viewed.

described), which direction is downwardlyas Another circular boss 38,-on the base A, whose uppermost surface is slightly lower than the uppersurface of the concentric boss 28, as Figs. '1 and 2 are viewed, has anannular groove 32 upon its upper surface. A radially extending raisedportion 84 has an end joining a portion of the outermost curved surfaceof the boss 38 and-the other end of the radially extending raisedportion terminates near the curved peripheral surface of the base A. Thegroove 82 serves as a resting-place for a. washer or ring-likeelectrical conducting member 88 whereby the washer 38 will not belaterally displaced, and the raised portion 84 serves to support the tab48 of the washer. A stop member 42, which is comprised of a-stud ofelectrical conducting material, has one end 48 passing through the tab48, through the base A, through one end of the middle terminal 24, andthrough a small copper washerinorder to retain the tab and the terminalboth mechanically and electrically together on resistance element,generally designated as B.

The inner diameter of the resistance element abuts against the curvedbounding surface of the raised boss 38 to prevent lateral displacementor shifting of the resistance element when the contact shoe is moved.Openings 50, 5! through each end of the resistance element 13 arealigned with openings 82, 83, respectively, in the base. A flat headholding rivet 54 passes through the aligned openings 88, 82 in theresistanceelement and the base, respectively, through one end of theelectrical conducting terminal 23 and, also, through a washer, so thatwhen the outside end of the rivet is expanded, one end of the resistanceelement, the base, theterminal 23 and the washer are secured together.Thus, the resistance element and the terminal 28 are electricallyconnected together by the rivet. Another rivet 55, connected in a mannersimilar to the rivet, holds the other end of theresistance element inelectrical contact with the terminal 25.

The control shaft I8 is journaled in the bore of the bushing I8 as wellas the central bore I2 of the base A, and at one end it is adapted tohave a knob (not shown) attached thereto, or it may have a central slotfor the reception of the flexible cable (not shown) or a key (notshown).

Intermediate the ends of the shaft i8 is a circumferential groove 58 forthe reception of a split or (i-washer 88, the latter prevents the shaftl0 from moving inwardly by engaging an end of the bushing. Thus, theshaft is prevented from moving in one longitudinal direction by theC-washer 88 which engages one end of the bushing i8 and is dinaldirection by the washer 28 and other means,

. hereinafter described, which engages the boss 28 of the base.

The other end 82 of the shaft I 8 is of adiameter that is smaller thanthe diameter of the majorportlon of the shaft, and upon the outermostportion of the shaft is a substantially semi-circular segment 84 whichserves as a key for a metal friction clutch or disc spring member,generally designated as C. The metal spring clutch member C has acomplementary semi-circular opening to interilt with the segment "84,and-the metal into 'enagement with the electrical conducting,

adjacent the central opening of the spring clutch member rests upon ashoulder 60 of the shaft I0. By compressing various portions .of thesegment 84, as at 81, Figs. 1 to 4, to engage the friction disc springmember C, the latter member is securely fastened to the shaft andrevolves in unison therewith. The spring clutch member C has aperipheral flange 68 offset slightly from the central portion 10.

When the flange 68 is mountedto bear against a fibre friction discmember, generally designated as D, the latter being positioned to extendat right angles to the longitudinal axis of the shaft, the flangelikewise extends at right angles to the longitudinal axis of the shaftand presses against the friction disc D. The disc D has a centralaperture which loosely interfits with the shaft end 62. Thus, thefriction disc D is not directly attached to the shaft.

The friction clutch member defined by the friction disc spring C and thefriction disc D serves to couple the shaft I to the volume control headF, the latter being hereinafter described in considerable detail.

A combined disc spacer and coupling, generally designatedas E, has awide main body portion I8 of metal or of insulating material, and anupper end I4 of a smaller diameter than the body I6, see Fig. 3. Thecurved surfaces of the body portion I6 and the end portion I4 are joinedby an annular fiat surface which engages the lower surface of thefriction disc adjacent the opening 12, when the opening I2 and the endI4 are fitted together. A hollow cylindrical metal rivet I8, of adiameter less than the diameter of the body "I8 of the spacer andcoupling E and having its bounding surface about the couplingslongitudinal axis is joined to and projects from the lower end of thespacer and coupling body portion 18.

The rivet member I8 passes through an opening in the volume control heador disc-like member F, comprised of insulating material, and the rivetmember I8 also passes through an opening at one end 90 of the pressurearm, generally designated as G, and after the rivets outside end isswedged over or expanded, the spacer is firmly held in position.

The disc-like member or volume control head F carries the contact shoepressure arm G, it also moves a resistance element contact member orshoe, generally designated as H, and moves a sliding electrical contact80 for leading the current from the contact member H to the washer 38,the latter in turn being connected to the terminal 24.

The control head F has a central aperture 8| which loosely interfitswith the reduced end 62 of the shaft I0; and the control head has amajor arcuate edge 82 which extends for approximately 266 and a minorperipheral extending edge 84 subtending the angle of (360 minus 266) 94the minor peripheral edge protrudes radially outwardly so that itsbounding edges 85, 85 may abut against the stop 42 to limit the movementof the control head.

A second combined spacer and coupling member, generally designated asEI, is constructed similarly to the member E and is symmetricallypositioned upon the control head F to retain the other arm 92 of thepressure member. The arm 02 does not terminate under the spacer memberEI but is continued so that its end 94 is freely extended. Thus, thefreely extended arm 94 is fulcrumed at a single position therebypermitting a limited degree of resiliency. This resiliency is employedto press the electrical contact pin 80 washer 38.

The pressure arms 90 and 92 merge into a con tact shoe engaging member96. The shoe engaging member has a trough formed on its upper surface sothat its lower surface has a downwardly extending tongue 08 convex aboutits transverse axis and straight along its longitudinal axis.

Within a rectangular recess I00 of the volume control headis positionedthe U-shaped contact shoe H. More specifically, the U-shaped deformablecontact shoe has substantially parallel legs I02 and I04 joined by abight-like portion I08 that engages the resistance element B. Theuppermost surface of each leg is pressed by the tongue 98 so that a goodelectrical contact is made by the bight-like portion I06 upon theresistance element, and the bight-likeportion wipes the resistanceelement as it moves thereupon, thus removing any corrosive substancethat may form, and always establishing a good electrical contact. Thelegs I02, I04 of the contact shoe H may diverge slightly so that whenthey are inserted into the recess I00, each leg abuts against an edge ofthe recess whereby there will be no lost motion between the volumecontrol head and the contact shoe, nevertheless the contact shoe mayadjust itself upon the resistance element. The bight-like portion I06that engages the resistance element may have its engaging surface eitherflat or arcuately formed; the latter reduces the contact area and soincreases the effective length of the resistance element.

A recapituation of the operation of the illustrated device embodying myinvention is as follows:

With the various elements comprising the friction clutch rheostatconnected as illustrated in Figs. 1 and 2, movement of the control shaftI0 either in a clockwise or counterclockwise direction rotates thefriction disc spring C in a clockwise or counterclockwise direction. Nowassuming that the edge 86 of the control head abuts against the stop 42and the shaft I0 is rotated in a counterclockwise direction as thedevice in Fig. is viewed. Since the control head remains stationary asthe friction disc spring revolves, the friction disc D is prevented frommoving as it is keyed to the volume control head F by means of thecombined spacer and couplings E, El. It is to be observed that thefriction disc spring may be revolved a multiple number of revolutionswithout injuring the mechanism of the rheostat.

Now assume that the direction as above mentioned is reversed and theedge 86 moves from the stop' member 42. As the shaft is revolvedclockwise, the frictional force between the friction disc spring C andthe friction disc D moves the volume control head. The control head Fcarries with it the contact member H which slidably engages theresistance element B, and since each end of the resistance element issuitably connected to terminals 23, 25, the voltage will be varied dueto the R. I drop between the contact member and each terminal as thecontact member changes its position with respect to either of theterminals. In order to secure the appropriate derived circuit, it isnecessary to carry the current from the contact shoe H to the terminal24 of the derived circuit. The current is taken from the contact shoe bymeans of the tongue 08 of the pressure arm G engaging the contact shoe,the current continuing to pass through the arm 92 to the end 94 whichengages the electrical conducting pin 00. As the control head revolvesthe pin is in continuous electrical engagement with the washer 88, thewasher in turn being connected to the tab 48 which is electricallyconnected to the terthe friction disc spring C and the friction disc Dmove in unison.

Although I have described and illustrated one embodiment of my'inventlonI illustrate another embodiment of my invention in Figs. '7, 8, and 9wherein a contact shoe pressure member as well as a rotary electricalcontact member is shown.

In the modifications illustrated in Figs. 7, 8 and 9, a shaft II8 has areduced circular end I82 integrally formed therewith. Projecting fromthe upper end of the reduced end is another reduced section whichprojects through the friction disc spring C.- Upon the upper surface ofthe friction .disc spring C is a washer which firmly bears the discspring C against the shoulder formed at the end of the reduced memberI82 after the end of the shaft is swedged over to securely lock thespring disc D to the shaft I I8 so that the friction disc spring C willnot turn with respect to the shaft. The outer fiat surface of thefriction disc D bears against the flange of the disc spring C and isloosely mounted about the reduced member I82. Combined spacers andcouplings E, El space and connect the friction disc D to the volumecontrol head, generally designated as Fl. The control head Fl isconstructed similarly to the control head F (Fig. 3) except the contactshoe opening the control shaft opening. and the combined spacers andcouplings E, El are located on the same diameter.

. The control head rests upon a fibre washer I28.

- member I88, which actually engages the contact shoe, than the ends ofthe U.

A depending tongue I88 of arcuate cross-sectional area and constructedsimilar to the tongue 88, Figs. 2 and 3, also is formed in the shoeengaging member I 88.. The base I88 of the pressure arm has an openingtherein which interfits with the rivet portion of the spacer E. Therivet of the spacer E also passes through an opening in a metallicrotatable brush 288' and when the end of the rivet is expanded, then therotary aoeauo so that they frictionally slide in engagement with thestationary washer 88 without ripping. or unduly scraping the member onwhich it rubs.-

In Fig. 10, I disclose two volume controls V, VI

arranged in tandem wherein each resistance element contact member onlycar'rbe moved less than 360 and wherein the single control shaft may berotated clockwise or counterclockwise 360 or more. Referring now morespecifically to Fig. 10 wherein similar designations refer to partshereinbefore described, a controishaft, generally designated as J, has acircular main body portion 888 -of a diameter to fit within the that oneface of the washer 28 just abuts or clears the uppermost statue of thebase A.

From the reduced portion 884 of the shaft 8 is still another reducedcircular portion 888. This reduced portion of the shaft 888 is ofconsiderable length and extends a distance substantially. equal to thedistance between the two volume control heads F, F2. I

The reduced portion 884 ofthe shaft loosely interfits with the centralopening in the volume control head F and the turning torque for movingthe control head is supplied from the control shaft to the control F bya friction clutch, as shall hereinafter be described.

The reduced portion 888 of the shaft loosely interfits with the openingin the volume control head F2, the latter being constructed similarly tothe control head F. The turning torque for the control head F2 isindirectly supplied to the.

control head by the friction clutch, as shall be hereinafter described.The volume control heads F, F2 are rotatable in parallel planes aboutthe same axis. 1

Encircling the reduced portion 888 of the shaft is a helical expansionspring, generally designated 'as K. The spring presses against each ofthe parallel volume control heads F, F2 tending to separate them in adirection along the longitudinal-axis of the shaft. However, the lowervolume control; head F is limited in movement in a downward direction byabutting against the washer 28, the latter in turn being limited byengaging the shoulder 882 and the upper volume control head F is limitedin movement in an up-' ward direction, as Fig.- 10 is viewed, byabutting against a washer 888 which is fastened to the shaft J by havingthe uppermost end 8I8 of the shaft swedged over. Hence, the shoulder 882and the expanded end 8I8 not only serve as stop members but also serveto provide the positive force to the frictional coupling which has asits slip members the volume control heads F and F2. The volume controlinstrumentalities are mounted in operable position upon the base A whichis substantially enclosed by a metallic casing, generally designated asL. The metallic casing has suitable holding lugs or ears and may beconstructed similarly to the casing as described in my copendingapplication, Serial No. 701,802 filed December 11, 1933.

Upon the fiat surface 8 of the cover L is a central opening to'accommodate the holding bushing for the base, generally designated asAI.

tion of the cover so that a rivet portion of a lug 3l2 may be insertedtherein. The lug "2 has the rivet integrally formed therewith so thatafter the rivet is inserted in its complementary opening in the cover Land after having its end expanded the lug 3i2 firmly grasps the cover.An opening or recess 3 in the base Al receives the other end of the lugso that when the lug M2 and the recess 3 interfit they prevent rotarymovement of the base Al with respect to the cover L since the latter inturn is prevented from rotating with respect to the base A by suitablestop members.

The casing L being constructed of metal serves as an electromagneticshield since the stray lines of the magnetic force will be dissipated asheat within the metallic casing J, and it the casing J is grounded orconnected to a place in the electrical circuit where the electricalpotential is zero, then the cover also serves as an electrostatic Ishield.

The operation of my invention as disclosed in Fig. 10 is as follows:

The volume control head islimited in movement by the stop member 42 ofFig. 5 having either edge 35 or the edge 36 abutting therewith. Thislimits the distance of movement the control head between the majorportion of the circle between the edges 35 and 83 which in this case isapproximately 266.

Assume that the edge 86 of the control head abuts against the stop 42and the shaft J is rotated in a counterclockwise direction as the deviceis viewed when it is in a position similar to that illustrated in Fig.5. Both volume control heads F, F2 remain stationary as the shaft isrevolved in a counterclockwise direction, since each volume control headabuts its cooperative stop member.

Now assume that the direction of the shaft is turned in a clockwisedirection. As the shaft G is revolved, sufilcient friction existsbetween the washer 308, the upper control head -F, the spring K, and thelower control head F to move both volume control heads F, F2 over and inengagement with their respective resistance elements. The deviceoperates for the remainder of its cycle of operation similar to thedevice illustrated in Figs. 1 to 9.

Referring now to Fig. 11, I show dual tandemarranged volume controlshaving a helicalspring-type of friction clutch, arranged together with asnap switch, all of the volumecontrols as well as the snap switch arecontrolled from the same control shaft. The structure of each of thedual controls is similar to that described in conjunction with Fig. 10,but upon the upper metallic housing a snap switch is mounted. The snapswitch has a forked trigger actuator 3H5 operatively connected thereto.

A lug 3; is suitably fastened upon the upper volume control head Fl totransiently engage one arm of the forked trigger 3l6. The amount offriction produced by the spring K must be greater than the opposingresistance produced by the snap switch spring 320 in order to opera- 5tively move the volume control head. By employing a spring K orsuflicient strength so that theArictional coupling force between thecontrol member and the volume control head is large, there will besubstantially no phase difference in the two volume control heads, usingthe word "phase in the sense that the volume control heads 1", F2 do notmove identically with respect to the same starting point. Thus, thevolume control head F will move in synchronism with the control head F2even though there is a greater opposing i'rictional force opp in themovement of the volume control head Ff than the irictional forceopposing the movement of the volume control head I".

The switch mechanism is mounted within a chamber of an insulator base,the base preterably being comprised of a molded phenolic condensation'product. A pivot 322 is located adiacent the peripheral edge of thechamber and about the pivot is loosely mounted the fork trigger actuator3l3 and one end of a rectangular strip 324. The strip 324 ,has its otherend 325 located within a recess 326 on the base. The side edges 321 and323 of the recess 328 limit the rotary movement of the strip 324. Thetorsional spring 323 for rapidly moving the strip from one extremeposition to the other extreme position has one leg suitably connected tothe strip and its other leg suitably connected to the outermost free endoi. the trigger.

Upon the flat wall or the switch housing and centrally located thereinis a pivot 332 which carries a bridging element having five arms 334,335, 333, 331, and 333 radially extending from its center. The arm 333has its free end bent at right angles so that the tip interflts with anopening in thestrip 324. The ends of the arms 334, 335, 331, and 338 areadapted to wipe into engagement with rivets, which are connected to theoutside terminals. Rivets 3, 342 are'connected to the outside terminal344 and rivets 343 and 343' areconnected to the outside terminal 343.Thus, as the strip 324 is oscillated from one extreme position to theother extreme position, it moves the lever arm 336, because of theinterfltting tip 343 and the recess, about the pivot 332. Therefore, inconsequence of the movement of the arm 336, the contact members willwipe into or out of engagement with the contact members.

Movement of the trigger does not actuate the bridging members until themedial axis of the closed end oi! the spring passes slightly beyond deadcenter. The trigger compresses the spring arms 0! the torsional springtogether, and the to eliminate any short circuit from occurring betweenthe rheostat casing and the switch mechanism elements. I

A sheet of insulation is also disposed upon the movable strip.

Upon the rim of the switch housing extend studs 3'3, 3", see Fig. 14,which facilitate loprising a constant resistance main circuit and aderived circuit of variable resistance. However, the unit may readily beemployed as a variable resistance by using only two terminals instead ofthree terminals.

. The friction clutch type of rheostat or the combined friction clutchrheostat and switch unit may be suitably adapted for the home-type ofradio where the rheostat or the rheostat and switch unit may be mountedupon the "chassis, which carries the signal receiving circuits andapparatus, while the control knob is mounted at an angle with respect tothe rheostat shaft and where a flexible shaft suitably connects therheostat and the control knob; the latter being mounted upon the radiocabinet.

Although this invention has been-described'in considerable detail, suchdescription is .-intended as illustrative rather than limiting as theinvention may be variously embodied.

My invention, therefore, is not restricted except as far as it is madenecessary bythe prior art and by the spirit of the appended claims.

I claim as my invention:--- 1. An adjustable resistance devicecomprising a base of insulating material, a flat resistance elementmounted upon said base, a central circular boss on said base having adiameter of substantially the same diameter as the inner diameter of theflat resistance element, a groove upon the upper surface of said boss, awasher of electrical conducting material within said groove, a controlshaft having a friction disc spring securely mounted upon one endthereof, a friction disc loosely mounted upon said control shaft andengaged by said friction disc spring, a volume con trol head parallel tosaid friction disc and loosely mounted upon said control shaft and acontact shoe opening therein, a plurality 'of spacer members betweensaid friction disc and said volume control head. said spacer memberssecurely mounted to said volume control head and connected to saidfriction disc whereby rotatable movement of the friction disc rotatesthe volume control head, a pressure arm connected to said volume controlhead, a resistance element contact shoe interfltting with said contactshoe opening and engaging said resistance element-and being pressedagainst the resistance element by the said pressure arm, said contactshoe being rotatable upon rotation of said volume control head, andmeans to limit the movement of said con-' tact shoe, .said control shaftbeing unlimited "in" clockwise or counterclockwise movement.

2. A volume control comprising a resistance:

element, a contact shoe for selectively engaging the resistance elementalong its length, a plurality of terminals, one of said terminalsconnected to one end' of said resistance element and another terminalconnected to the other end of the resistance element therebyestablishing a constant resistance main circuit between the said endterminals, an electrical brush member, a pressure member engaging saidcontact shoe and electrically connected to said brush member, said brushmember being adapted to rotate in" unisonwith said pressure member andhaving'a resil'-"- iently mounted concave prong, a stationary a'nnularwasher of electrical conducting material: engaged by said movableconcave prong, one of said terminals electrically connected to saidstationary washer thereby forming one side of the derived circuit, acontrol shaft, and a friction clutch interposedbetween said shaft andsaid contact shoe. i

3. A volume control comprising a resistance element, a contact shoe'forselectively engaging the resistance element along its length, aplurality of terminals, 'one of said terminals con- .nected to one endof said resistance element and another terminal connected to the otherend of the resistance element thereby establishing a constant resistancemain circuit between the said end terminals, an electrical brush member,a pressure member engaging said contact shoe and electrically connectedto said brushmember, said brush member being adapted to rotate inunisonwith said pressure'member and having a resiliently.

' tandem, and a snap-switch having a forked trigger, a single controlshaft for controlling the two rheostats and the snap switch, each ofsaid rheostats including aresistance element, a rotor member, and acontact shoe movably connected to said rotor, each of said rotors freelyrotatable about said control shaft, a helical spring interposed betweensaid rotor members and imposing a force upon said rotor members, meansengaged by said rotors and movable by said control shaft whereby thefrictional force between the said means and said rotors will move saidrotors, and a stud on one of said rotors and cooperable with said forkedtrigger of said switch whereby'the switch may be actuated to open orclosed circuit position at a predetermined definite transient movementof said stud.

* 5. A variable resistance device comprising a resistance element, aU-shaped deformable contact member for engaging said resistance element,a pressure member having a depressed tongue which tongue is inengagement with an upper portion of each leg of said U-shaped member, aninsulation member carrying said pressure member and having an opening tocomplementarily receive the contact member, the legs of said U- shapedmember extending above the upper surface of said insulation member, andsaid insulation member being adapted to push against each leg of saidcontact member whereby the contact membermay selectively engage theresistance element between its ends.

6'. In combination, two rheostats arranged in tandem, each of-saidrheostats'including a re?- sistance element, a rotor, and a contact shoemovably connected to' said rotor, a single control shaft for adjustingthe contact shoe of each rheostat, each of said rotors freely rotatableabout said control shaft, frictional stop members rotatable with saidshaft, and a helical spring interposed between and engaging said rotorsand imposing a force upon said rotors, the frictional force-between eachrotor and said frictional stop member being sufllcient to exert aturning torque on .said rotor upon the turning of the control tpredetermined portions of arcuate movement of said control.

7. A rheostat comprising a base of insulating material, a fiatarcuate-shaped resistance element mounted upon said base, an annularboss formed on said base whereby theinner surface of said arcuate-shapedresistance element is adapted to abut against the curved surface of saidboss, means to hold the terminal ends of said resistance element firmlyto said base, a U-shaped deformable contact member for selectivelyengaging said resistance element along its length, a pressure arm havinga depressed tongue which tongue is in engagement with an upper portionof each leg of said U'-shaped member, an insulation member carrying saidpressure arm and having an opening to complementarily' receive theU-shaped contact member, the legs of said U- shaped member extendingabove the upper surface of said insulation member, said insulationmember being adapted to push against each leg of said contact memberwhereby the contact member may selectively engage the resistanceelement, a groove on the upper surface of said boss, a ring-like memberof electrical conducting material interfitting with said grooves wherebythe ring-like member will not be laterally displaced, and means forelectrically connecting said U-shaped member to said ring-like member.

8. In combination; two rheostats arranged in tandem; each of saidrheostats including a resistance element, a rotor, and a resistanceelement contact shoemovably connected to said rotor; a single controlshaft for adjusting the contact shoe of each rheostat; each of saidrotors freely rotatable about said control shaft; frictional couplingmembers rotatable with said control shaft and engaged by said rotors;and a helical spring interposed between and engaging said rotors andpressing said rotors against said coupling members rotatable with saidcontrol shaft whereby the force created by the spring upon the rotorsand their cooperative coupling members will be sufficient to exert aturning torque on'said rotors upon the turning of the control shaft.

9. A variable resistance device comprising a resistance element, aU-shaped deformable contact member for engaging said resistance element,a pressure member, an insulation member carrying said pressure memberand having an opening to complementarily receive the U-shaped member,the legs of said U-shaped member extending above the upper surface ofsaid insulation member, an upper portion of each leg of said U-shapedmember engaged by a portion of said pressure member, and said insulationmember being adapted to push against each leg of said contact memberwhereby the contact member may selectively engage the resistance elementbetween its ends.

CLARENCE J. HATHORN.

